Freedoom is a project to create a complete Doom-compatible IWAD file
which is free software. The IWAD file is the file used by Doom which
contains all the game data (graphics, sound effects, music, etc.). While
the Doom source code is free, you currently still need one of the proprietary
IWAD files from id in order to play Doom. Freedoom aims to create a
free alternative. It has already succeeded in creating a complete set
of replacement textures for the original Doom games, as well as a large
amount of extra material (sound effects, graphics, sprites, etc). The website recommends using PrBoom-Plus and/or Odamex. The gameplay mechanics (monster and weapon behavior, etc.) are identical to the original Doom games, but completely original artwork is used. Phase 1 - This IWAD contains levels arranged into four episodes, similar to the original Ultimate Doom. This allows mods for the original game to be played. Phase 2 - This IWAD contains levels in a flat linear progression, similar to Doom 2. This allows mods for Doom 2 and Final Doom, which consists of two standalone megawads: TNT: Evilution and The Plutonia Experiment, to be played. FreeDM - This IWAD, compatible with the original Doom engine, is a collection of original deathmatch levels, using the same artwork as the main Freedoom IWADs. Also, this one can be used to play mods for Doom 2 and Final Doom.